There have heretofore been widely used DC/DC converter apparatus as switching power supplies having switching devices such as MOSFETs, IGBTs, or the like.
For example, there has been proposed a vehicle (hereinafter referred to as an “electric vehicle”) incorporating a motor as a propulsive drive source, and a DC/DC converter apparatus for increasing and reducing a DC voltage. The DC/DC converter is connected between an electricity storage device and the motor, which is energized by an inverter. On the electric vehicle, when the motor is energized, voltage across the electricity storage device is increased by the DC/DC converter apparatus and applied to the inverter. When the motor regenerates electric power, the regenerated voltage from the inverter is lowered by the DC/DC converter apparatus and applied in order to charge the electricity storage device.
There has also been proposed a vehicle (hereinafter referred to as a “fuel cell vehicle”) as another form of electric vehicle. The fuel cell vehicle includes a fuel cell directly connected to a motor, which is energized by an inverter. A DC/DC converter apparatus for increasing and reducing a DC voltage is connected between an electricity storage device and a junction between the fuel cell and the motor. The fuel cell is used as a main power supply, whereas the electricity storage device is used as an auxiliary power supply for assisting the main power supply.
On the fuel cell vehicle, when the motor is energized, voltage across the fuel cell and voltage across the electricity storage device, which has been increased by the DC/DC converter apparatus, are added together, and a sum voltage is applied to the inverter. When the motor regenerates electric power, the regenerated voltage from the inverter is lowered by the DC/DC converter apparatus and applied in order to charge the electricity storage device. If the electric power generated by the fuel cell is excessive, then the electrical power is lowered in voltage and applied in order to charge the electricity storage device.
The DC/DC converter apparatus comprises a semiconductor module (switching module) including switching devices and diodes. In particular, the switching devices need to be cooled sufficiently because the switching devices generate a considerable amount of heat when energized. Generally, cooling apparatus having cooling liquid passages therein have been used. For use in applications on vehicles, it is important for the cooling devices to meet both requirements of providing sufficient cooling capability as well as being small in size.
For example, Japanese Laid-Open Patent Publication No. 2004-349324 proposes a cooling apparatus in which an IGBT module is disposed directly on a flat base plate together with cooling fins. In the cooling apparatus, the cooling fins are disposed at positions corresponding to chips that act as heat emission devices. Cooling fins that are positioned immediately before the heat emission devices along the direction in which the cooling liquid flows have cutouts therein, so as to provide edges at cooling liquid inlets of the cooling fins for disturbing the cooling liquid and thereby increase the cooling effect.